1. Field of the Invention
This invention relates to method and devices for the regulation of cell proliferation and gene expression. In particular, the invention relates to the inhibition of photoaging of the skin.
2. Description of the Background
Chronological aging brings about a group of changes in the appearance of human and mammalian as well as changes in the structure and function of the skin. All living cells, tissues and organs also undergo changes associated with chronological aging. Since the human skin is an organ that is highly visible, the changes associated with chronological aging are readily apparent and visible. These changes are reflections of the underlying structural and functional changes.
The phenotype associated with chronological aging of the skin is an outward reflection and expression of the genotypic changes, which occur within the cells of the skin. The most widely appreciated form of skin aging is that which is produced by over exposure and repeated chronic exposure to sunlight and is generally termed photoaging. More specifically certain portions of the ultraviolet A (UVA) and ultraviolet B (UVB) and have been determined to be the principal causative factors of what are associated with photoaging.
For many years it was thought that photoaging occurred through a different mechanism of action and was somehow different than chronological aging. However, more recently it appears that photoaging and chronological aging may share similar, if not identical pathways.
Solar radiation is composed of ultraviolet (UV), visible and infrared, light. Current conventions divide UV radiation into UVA (320-400 nm), UVB (290-320 nm) and UVC (<290 nm). UVC radiation is blocked by ozone in the stratosphere and does not reach the earth's surface, but can be generated by germicidal lamps and other machinery. UVA and UVB sunlight do reach the earth and are believed to be the principal agents of photoaging. UVA radiation is further subdivided into UVA 1 and UVA 2. While UVB has been believed to be the primary agent for photoaging, it is now appreciated that certain wavelength ranges within the UVA rays also contribute to changes associated with photoaging.
UVA and UVB light exposure to human skin triggers a series of molecular events including the induction of reactive oxygen species (ROS) in the skin. Through a series of cell signaling events collagen production is down-regulated and various enzymes known to degrade structural proteins in the skin up-regulated. The net result of this is a decrease in collagen and the production of wound. The skin's reaction to UVA or UVB (or combined) wounding is to repair the wound through the skin's wound healing mechanism. Typically these wound repair mechanisms are imperfect which is considered by many to be a solar scar. After many years of the UVA or UVB wounding of the skin, chronic solar scarring develops which manifests itself in the visible phenotypic changes termed photoaging, which might also be considered the visible outward evidence of solar scars.
Photoaging of the skin may occur through acute injury at higher levels, such as what one associates with sunburn. This triggers an inflammatory process in the skin and the associated cellular mechanisms. There is also a more chronic low-level type of injury that does not produce a sunburn reaction, but which produces the changes of chronic photoaging. Other processes, which are known to decrease collagen production and increase collagen-dissolving enzymes, such as tobacco smoking, also are associated with changes that visibly appear, similar to the photoaging from UVA/UVB light. This can be seen strikingly in photographs of identical twins wherein only one twin smoked tobacco for many years.
UVB radiation in sufficient doses produces reddening or sun burning of the skin. The threshold level is typically described as minimal erythemal dose (MED), typically produced by 290-300 nm UVB wavelengths. As the wavelengths increase they become much less likely to produce the redness and burning reactions and indeed wavelengths of 320 nm are about 100 times as powerful as wavelengths of 340 nm approximately 100 times less powerful than the 290-300 nm range of producing erythema and sunburns. The total UVB exposure is more related to the appearance of photoaging and sunburns are more likely to trigger malignant changes in the skin such as malignant melanoma. In contrast, UVA radiation can produce redness, but also produced tanning and these are the wavelengths typically used for the so-called tanning beds. UVA radiation is a longer wavelength and is proportionately greater in the early morning and late afternoon than the UVB rays, which are typically most predominant and intense at the midday summer sun time exposure period. UVA radiation may also penetrate certain sun blocks and certain sunscreens and also window glass on automobiles, thus accounting for the frequently observed greater wrinkling, brown pigmentation and redness and overall aged appearance on the left side of the face than the right in patients who occupationally or recreationally spend considerable time driving a left hand drive motor vehicle.
In sunny countries with fair complexioned populations, such as Australia, where right hand drive motor vehicles are used, these changes are typically seen on the right side of the face. The patterns of photoaging are determined by which areas of the body are anatomically more chronically exposed to sunlight. Thus, the face, neck, back of hands, upper chest, lower arms, lower legs and depending on hair styling and density, ears and balding areas manifest the greatest photoaging changes.
The chronological changes and photoaging changes typically are manifest by fine lines and wrinkling of the skin, a coarser, crepey texture to the skin, skin laxity and skin sagging, uneven pigmentation, brown splotchy pigment, loss of skin tone, texture and radiancy, bruising and sallowness. The skin is composed of several layers, the outermost layer is called the stratamocornium (SC), the next layer is the epidermis (EPI), and underneath the epidermis lies the dermis (DER). The outer SC serves primarily a barrier function to protect the skin from environmental exposure and also to help minimize water loss from the skin. The epidermis serves many important and diverse roles as does the dermis. The dermis contains the principal structural proteins of the skin. These proteins are collagen, elastin and ground substance. They are manufactured by the fibroblast cells within the dermis. Fibroblast cells control the activity to produce these proteins as regulated by a complex and relatively well defined series of cell receptors and cell signaling mechanisms.
The proliferation of these cells is also an important activity. For example, the dermis also contains blood vessels, nerve fibers, oil and sweat glands, hair follicles and many other important components. There is a remarkably complex inner communication through cell signaling in the cells of the skin. Fibroblasts produce what are termed pro-collagen fibers, which are then insymmetrically assembled into collagen fibers, and form bundles within the dermis. Other molecules, such as decorin affect the function of the collagen. There are various sub-types of collagen fibers such as Collagen I, III, etc., within the body. Collagen I comprises approximately 85% of the skin and Collagen III approximately 10%. However, in photoaged skin the amount of Collagen I decreases so the ratio of Collagen III/I is altered.
There are also a variety of enzymes termed matrix metalloproteinases (MMP) which play important roles in aging skin. Fibroblasts also have important functions in wound healing with the removal of damaged structural ECM and the repair and production of ECM. The Collagen I is degraded principally by MMP 1 (collagenase). There are a variety of MMP enzymes, which degrade one or more of the structural proteins in the skin. While these degrading MMP enzymes serve an important role in removing damaged skin (for example, in wound healing), their activation and synthesis in increased quantities in normal skin helps contribute to the changes seen in both chronological and photoaging. Likewise, if the production of Collagen I is decreased or diminished, this results in changes which are associated with chronologically or photoaged skin. Aging or senescent fibroblasts may exhibit decreased synthesis of Collagen I and increased synthesis of MMP 1. Similar changes are seen with UVA/UVB exposure. Other environmental agents may produce similar changes.
Certain drugs, therapies, chemicals, active agents have been demonstrated to reverse the appearance of or phenotype of a chronologically aging or photoaging skin. Some topically applied agents serve as a physical or optical barrier either by reflection or absorption of ultraviolet light thus protecting the skin. There are also enzymes that have been shown to actually repair the DNA dimers which are produced from UV damage. Other topically applied or oral or systemically applied agents have been shown to improve the appearance of the skin. One of the classic and well-known agents is a topical Vitamin A derivative termed Retinoids. Numerous studies have demonstrated the ability to improve the appearance or phenotype of photoaged skin with the use of all-trans retinoic acid (RA). Many of the cell signaling pathways involve the mechanism of action of RA and also Retinol (RO). Much of the mechanism of action of RA in the cell signaling pathways appears to produce anti-aging effects.
One of the goals of some current anti-aging therapies is to increase production of collagen in the ECM and the dermis of the skin. Some believe collagen I is the more desirable form of collagen to increase. There is some support for this since photoaged skin has less desirable visco elastic properties and this is thought in part to be due to the increased proportion of collagen III to collagen I. Other anti-aging approaches indicate that reducing the activity or production of the degrading enzymes in the ECM will similarly produce an anti-aging effect in the appearance of the skin. Doing a combination of both is even more beneficial. An analogy one might make is the production of new collagen I and that of freshly newly fallen snow. The amount of accumulation of the fresh snowfall is dependent both on the amount of snow that is fallen as well as the amount of the freshly fallen snow which then melts. Thus one could envision an anti-aging therapy which stimulated new collagen production (newly fallen snow). When a piece of black asphalt in a parking lot abuts a piece of warmer black asphalt adjoining a colder piece of concrete or frozen ground, while the amount of new snowfall is equal in both areas, the amount of accumulated snow melted by the warmer asphalt is more than the amount of snow melted by the frozen concrete. If an anti-aging therapy stimulates collagen I production, but does not diminish MMP 1 activity, the net increase in collagen I will be smaller than if the MMP 1 activity is also decreased.
Historically there have been many approaches to restoring a youthful appearance to human skin for achieving anti-aging or age reversal therapies. Most methods utilize some form of triggering the body's own wound healing mechanism. The more destructive and traumatic methods use chemicals to peel off the stratum cornium epidermis and often a portion of the dermis or mechanically abrade the skin by sand papering or dermabrating or more recently use high-energy thermal lasers to vaporize or coagulate the skin. These methods have a prolonged and painful wounding period and require wound care. Patients typically must limit their daily social and business activities during the wound-healing phase. Subsequently the skin undergoes months or years of an ongoing wound healing and wound remodeling process, whereby damage is repaired and new structural proteins in skin are generated. These treatments typically amount to trying to produce a controlled entry to the skin and providing the wound care environment that minimizes the risk of scarring. These methods are notoriously known for producing many problems and sometimes even disfiguring scarring or catastrophic pigment changes in the skin. However, properly performed and with good wound care, many people achieved significant and sometimes dramatic anti-aging effects. Other gentler methods have become more popular in recent years which involve the classic plastic surgery lifting procedures and newer procedures termed non-ablative, where the outer stratum cornium and epidermis are not removed or blated from the skin, but are by various means and methods protected and left in tact. Non-ablative methods have typically been thermal in nature and through various means of laser light, intense pulsed light, radio frequency or microwave energy delivery then produced a thermal injury to the dermis. The theory behind these therapies is that this injury will result in a net increase in the desirable structural proteins, while not triggering, worsening, scarring or other complications. Results are occasionally traumatic but have been extremely variable with this therapy. The variability in individual wound healing repair mechanisms, overall health of body and skin, and many other factors contribute to this variability in results.
There are various topical agents that have been developed for anti-aging purposes such as Retinoic acid, topical Vitamin C, topical Vitamin E and other antioxidant and other anti-wrinkle creams and lotions. Many of these are well defined.
There is a need to improve the appearance of chronologically aged, photoaged, or environmentally damaged skin, but without producing the risk, complications, recovery time, pain, discomfort, wound care or other side effects traditionally associated with surgical, chemical, electromagnetic radiation and other types of therapies.